The present invention relates to treatments and compounds useful in subterranean formations, and, at least in some embodiments, to treatments and compounds for removing silica scale build-up.
Treatment fluids may be used in a variety of subterranean treatments, including, but not limited to, stimulation treatments and remedial treatments. As used herein, the term “treatment,” or “treating,” refers to any subterranean operation that uses a fluid in conjunction with a desired function and/or for a desired purpose. The terms “treatment,” and “treating,” as used herein, do not imply any particular action by the fluid or any particular component thereof. These subterranean operations include, but are not limited to, conformance treatments, hydraulic fracturing treatments, acidizing treatments, remedial treatments, scale removal and inhibition, and the like.
Acidic fluids may be present in a multitude of operations in the oil and chemical industry. Acidic fluids are often used as a treatment fluid in wells penetrating subterranean formations. Such acidic treatment fluids may be used in, for example, remedial operations or stimulation operations for oil and gas wells and hydrothermal wells. Acidic stimulation operations may use these treatment fluids in hydraulic fracturing and matrix acidizing treatments. Moreover, many treatment fluids include a water source that may incidentally contain certain amounts of acid, which may cause the treatment fluid to be at least slightly acidic. As used herein, the term “treatment fluid” refers to any fluid that may be used in an application in conjunction with a desired function and/or for a desired purpose.
These acidic treatment fluids are used in operations in subterranean formations comprising minerals, commonly clays, that are part of the native formation's mineralogy, which may react with other substances (e.g., water, minerals, treatment fluids, and the like) that reside in the subterranean formation in chemical reactions caused, at least in part, by conditions created by mechanical stresses on those minerals. These reactions are herein referred to as “stress-activated reactions” or “stress-activated reactivity.” One type of these stress-activated reactions may be diageneous reactions. As used herein, the terms “diageneous reactions,” “diageneous reactivity,” and “diagenesis” include chemical and/or physical processes that, in the presence of water, move a portion of the mineral in a subterranean formation and/or convert a portion of the mineral in a subterranean formation into some other form. A mineral that has been so moved or converted is herein referred to as a “diageneous product” or “diagenic product.” Any subterranean formation comprising a mineral may be susceptible to these diageneous reactions, including natural silicate minerals (e.g., quartz), man-made silicates and glass materials, metal oxide minerals (both natural and man-made), and the like.
Silica (silicon dioxide) appears naturally in a number of crystalline and amorphous forms, all of which are sparingly soluble in water; thus leading to the formation of undesirable deposits. Silicates can be salts derived from silica or the silicic acids, especially orthosilicates and metasilicates, which may combine to form polysilicates. Silica solubility depends on a number of factors including, but not limited to, pH, temperature, and ionic composition. Most silicates, except the alkali silicates, are sparingly soluble in water. A number of different forms of silica and silicate salt deposits are possible, and formation of deposits depends, among other factors, on the temperature and pH of the water. Silica build-up may readily adhere to any surface that it contacts, including the surfaces of the well bore and/or any equipment utilized during the subterranean operation. If a sufficient amount of silica build-up adheres to surfaces in the well bore or the equipment, it may, among other problems, prevent fluid circulation, or otherwise impede the effectiveness of a treatment. In addition, the precipitation and gelation of amorphous silica during an acidizing treatment can result in plugging of pores, thereby resulting in a porosity decrease that can be detrimental to production operations.
Existing methods of managing these silica build-up problems can be problematic. Some of these methods involve using additional acid to dissolve the silica build-up (e.g., amorphous silica or gelled silica) during a matrix acidizing treatment. The processes of dissolving aluminosilicate and silicate minerals, mainly clay minerals or silica scale, typically involve using acids such as HF or HCl alone or in combination with other acids including organic acids or any other suitable strong acid such as, for example, fluoroboric acid, methanesulfonic acid, chloroacetic acid, hexafluorophosphoric acid, phosphoric acid, hexafluorotitanic acid, and fluorophosphoric acid. A difficulty encountered with the use of additional acidic fluids is determining the type of subterranean formation in which they may function effectively. For instance, formations comprising high pressures, high temperatures, and/or certain minerals cannot be treated with excess acid without undesirable damage. Moreover, the introduction of additional acid may increase the complexity and cost of the subterranean treatment.